Circuit for detecting initial systole and dicrotic notch

ABSTRACT

Circuitry is disclosed for processing an arterial pressure waveform to produce during any one cycle a pulse corresponding to the initial systole and a pulse corresponding to the dicrotic notch. In a first channel, an electrical analog of the arterial pressure waveform is filtered and then compared to the original waveform to produce an initial systole signal. In a second channel, the analog is differentiated, filtered and fed through a gate controlled by pulses from the first channel to produce an electrical pulse corresponding to the dicrotic notch.

United States Patent [191 [11] 3,850,169 Gebben et al. v Nov. 26, 1974[54] CIRCUIT FOR DETECTING'INITIAL 3,498,292 3/1970 Jorgensen et al.l28/2.06 R SYSTOLE AND DICROTIC NOTCH 3,646,931 3/1972 Phelps et al.128/205 P [75] Inventors: Vernon D. Gebben, Bay Village;

John Webb, Jr North Primary Examiner-William E. Kamm Ridgeville both fOhio Attorney, Agent, or Firm-J. A. Mackin; N. T. Musial; J. R. Manning[73] Assigneez The United States of America as represented by theAdministrator of the National Aeronautics and Space [57] ABSTRACTAdministration, Washington, DC. C d l d f l I ircuitry 18 18C ose orprocessing an artena pres- [22] Flled- 1973 sure waveform to produceduring any one cycle a 21 1 327 921 pulse corresponding to the initialsystole and a pulse corresponding to the dicrotic notch.

[52] Us Cl 128/2 05 P 128/2 05 A In a first channel, an electricalanalog of the arterial [51] Int 5/02 pressure waveform is filtered andthen compared to [58] Fie'ld M 205 P the original waveform to produce aninitial systole 128/2 05 'E R signal. In a second channel, the analog is06 differentiated, filtered and fed through a gate controlled by pulsesfrom the first channel to produce [56] References Cited an electricalpulse corresponding to the dicrotic UNITED STATES PATENTS notch3,224,435 12/1965 Traite 128/205 M 11 Claims, 2 Drawing Figures 11 l5 l3l4 Y or L Y A 7 -T m 20 r, e

MULTIVIBRATOR CIRCUIT FOR DETECTING INITIAL SYSTOLE AND DICROTIC NOTCIIThe invention described herein was made by employees of the UnitedStates Government and may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to electronicprocessing circuits and is directed more particularly to circuitry forprocessing an arterial pressure waveform to produce one discreteelectrical signal that coincides with the initial systole and anothersignal which coincides with the dicrotic notch. Initial systole isdefined herein as the point in time at which the aortic blood pressurerapidly increases as a result of the heart pumping blood into the aorticartery. The dicrotic notch is the pressure disturbance caused by theclosure of the aortic valve.

In studying and treating patients having heart damage and heart disease,the rise and fall of blood pressure in arteries near the-heart is animportant parameter to be observed. Transducers are available whichconvert the arterial pressure waveform into an electric signal which maybe displayed on devices such as oscilloscopes or recorders. However,where automatic monitoring of the arterial pressure is desired, as forexample to provide a signal when the arterial pressure waveform deviatesfrom a prescribed pattern, computers are being utilized. Such computersrequire timing signals corresponding to the initial systole and dicroticnotch of each cycle of heart operation. Such apparatus must be operativeover a range of heartbeat rates between 50 and 200 beats per minute andmust operate reliably for a variety of waveforms that can result fromabnormal circulatory dynamics, from irregular heartbeatsm or frombreathing pressures. Detecting changes in slope of the arterial pressurewaveforms is not a satisfactory approach because extraneous oscillationsare also detected. The approach of using a signal which is initiatedwhen the arterial pressure exceeds its average value has thedisadvantages of producing late signals and false signals when thepressure wave oscillates through the average value.

OBJECTS AND SUMMARY OF THE INVENTION Still another object of theinvention is to provide an initial systole and dicrotic notch detectorcircuit which operates over a range of 50 to 200 heartbeats per minute.

Yet another object of the invention is to provide circuitry includingmeans for filtering an arterial pressure voltage signal and comparingthe filtered signal to the original signal to detect initial systoleeven in the presence of low frequency breathing disturbances.

Still another object of the invention is to provide circuitry thatproduces a discrete output signal each time that the low frequencyportion of the arterial pressure signal has a positive inflection duringthe period that begins the first time the pressure signal after initialsystole becomes less in magnitude than its filtered waveform.

A further object of the invention is to provide initial systole anddicrotic notch detecting circuitry which includes pulse widthdiscrimination circuitry to suppress effects of detrimental highfrequency disturbances.

In summary, the circuitry of the invention filters the arterial pressurewaveform to remove low frequency components and then compares thisfiltered waveform to the original waveform to produce a rectangularpulse whenever the original waveform is greater in magnitude than thefiltered waveform. These pulses are passed through a unidirectional lowpass filter and a comparator and then through a unidirectional couplingcircuit, the output of which is a discrete voltage pulse correspondingto the initial systole. The arterial pressure waveform is also passedthrough a differentiator, and a first order high pass filter to producea signal that is related to the second derivative of the arterialpressure waveform. This signal is passed through a comparator and to amultivibrator. The multivibrator is provided with reset signals from asecond multivibrator which is reset by the discrete systole pulses andset by the square pulses. The first multivibrator does not produce anoutput except for preselected ones of the pulses applied to the setinput. The output of the first multivibrator is fed through aunidirectional coupling circuit whose output is a discrete pulsecorresponding to the dicrotic notch.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of acircuit for detecting the initial systole and the dicrotic notch.

FIG. 2 is an illustration of the various voltage waveshapesfound atvarious points throughout the circuit of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring first to FIG. 2, thepulses shown at 20) and 2(0) are the desired outputs of the circuit ofFIG. 1 and correspond respectfully to the initial systole and dicroticnotch.

Referring now to FIG. 1, the circuitry above dashed line 10 provides aninitial systole detection channel while the circuitry below line 10provides a dicrotic notch detection channel. The systole channelcomprises generally a signal processing circuit 11, a comparator circuit12, an impedance matching circuit 13 and a pulse width discriminator 14which may include a unidirectional low pass filter I5 and a comparator16. An electrical signal corresponding to an arterial pressure waveformas illustrated by waveshape 2(a) is supplied from a transducer 17 to aninput means such as terminals 18 and 19.

Terminal 19 is connected to a circuit common point as at 20 whileterminal 18 is connected through a lead 21 to a positive input of anoperational amplifier A1 and also through a resistor R1 to a negativeinput of the operational amplifier Al. The negative input of theoperational amplifier Al is also connected through 21 capacitor C1 tocircuit common 20.

Resistor R1 and capacitor C1 comprise a low pass filter circuit whichremoves the oscillations 22 of waveshape 2(a) which begin at thedicrotic notch so that the waveshape applied to the negative input ofthe operational amplifier A1 is that indicated by the dashed waveshape.However, the principal purpose of the low pass filter is to causewaveshape 2(b) to lag waveshape 2(a) to provide cross-over points 24 and25 which establish the leading and trailing edges of pulses 23 and shownin FIG. 2(0). 1

The output of amplifier Al is directed through a resistor R2 to apositive input of an operational amplifier A2, a zener diode Z1 beingconnected between the positive input of amplifier A2 and circuit common20. The voltage waveshape applied to the positive input of amplifier A2is shown at 2(0) and includes square pulses 23 having leading edgescorresponding in time to the points at which waveshape 2(a) becomesgreater than waveshape 2(b) as indicated at points 24 and also havingtrailing edges corresponding in time to the points at which waveshape2(a) again becomes less than waveshape 2(b) as indicated at points 25.

The low pass filter comprising R1, Cl has no significant effect onbreathing frequency components which may be included in the arterialpressure wave. Therefore, breathing frequency components are presentequally at both inputs of amplifier A1. Because the input of amplifierAl is differential and provides an output when waveshape 2(a) minuswaveshape 2(b) is positive, the breathing frequency components canceleach other. Thus the output of comparator 12 contains no breathingfrequency components which might adversely affect the time of occurrenceof the desired output initial systole pulse.

The output of amplifier A2 is connected to the unidirectional low passfilter 15 and is also connected back to its own negative input toprovide a follower circuit which isolates filter 15 from the comparatorcircuit 12. Filter circuit 15 comprises a resistor R3 connected inparallel with a diode D1 between the output of amplifier A2 and'one sideof a capacitor C2, the other side of which is connected to circuitcommon 20. Diode D1, resistor R3 and capacitor C2 are connected to thepositive input of an amplifier A3 which has its negative input connectedto circuit common 20. The voltage waveshape appearing at the positiveinput of the amplifier A3 is shown at 2(d). The leading edges of pulses26 correspond to the leading edges of pulses 23 which are passed by thediode D1. However, the negative going trailing edges of pulses 23 areblocked by diode D1 causing the trailing edges of pulses 26 to decayexpenentially. Portions 27 of a pulse 26 which fall below circuit commonreference level cause the output of amplifier A3 to go negative asindicated at 29 in waveshape 2(e).

The output of amplifier A3 is directed through a capacitor C3 and thediode D2 to a terminal 30 of an initial systole output means which mayalso include a circuit common terminal 31. The capacitor C3 and thediode D2 comprise a unidirectional coupling circuit which passes onlythe positive going portions of waveshape 2(e) so that the signalappearing at initial systole output terminal 30 relative to 31 comprisespulses 32 each of which corresponds to the initial systole as shown bywaveshape 2(a). Output terminals 30 and 31 may be connected to asuitable computer 33 to provide an initial systole timing signalthereto.

In order to produce a pulse corresponding to the dicrotic notch of anarterial pressure waveform, the dicrotic notch detecting channel maycomprise generally a low frequency differentiator circuit 34, a firstorder, high pass filter 35, a comparator 36, and multivibrators 37 and38' which serve as gate means. The purpose of the differentiator circuit34 and the filter circuit 35 is to produce for the comparator 36 awaveshape which is essentially a second derivative with respect to timeof waveshape 2(a).

Differentiator 34 comprises an amplifier A4 having a positive inputconnected to circuit common 20 and a negative input connected to acapacitor C4 and a resistor R4 to the input signal terminal 18. Aresistor R5 and a capacitor C5 are connected in parallel relationshipbetween the negative input of amplifier A4 and its output to providefeedback. To prevent latch-up of amplifier A4, a pair of zener diodes Z2and Z3 may be connected in back to back relationship between the outputand the negative input of amplifier A4.

The filter 35 may be comprised of a capacitor C6 connected between theoutput of amplifier A4 and a negative input of an operational amplifierA5, a point between C6 and the negative input of amplifier A5 beingconnected to circuit common 20 through a resis- The comparator circuit36 processes the second derivative of waveshape 2(a) which, as indicatedpreviously, is applied to the negative terminal of amplifier A5, toproduce a waveshape as shown at 2(i). The comparator 36 includes theamplifier A5, a resistor R7 connected between the output of amplifier A5and one side of a capacitor C7 and a zener diode Z4 connected as shownfrom a point between R7 and C7 to circuit common as at 20. The positiveinput of an amplifier A5 connected to circuit common 20 completes thecomparator circuit 36.

The other side of capacitor C7 is connected through a diode D3 to a setinput of multivibrator 37 which serves as a gate means. The waveshapeapplied to set input 39 is shown at 2(1) and comprises pulses whichcorrespond to the positive going portions of the output 2(i) of thecomparator circuit 36. The negative going portions of waveshape 2(1')are, of course, blocked by the diode D3.

it will be seen that the waveshape 2(1) includes closely spaced pulses40, 41 and 42 and remotely spaced pulse 43. Each of these pulses resultsfrom some positive inflection in the arterial pressure wave 2(a).Accordingly, all the pulses except those corresponding to the dicroticnotch must be eliminated to obtain a waveshape as shown at 2(n) at anoutput 44 of the multivibrator 37. To this end, there is provided amultivibrator 38 providing a reset input 46 connected via a lead 5 tooutput terminal 30 and a set input 47 connected through a diode D5 and acapacitor C9 to output of comparator 12 which is also the positive inputside of A2. An output 48 of multivibrator 38 is connected through acapacitor C10 and a diode D6 to a reset input 45 of multivibrator 37.Multivibrator 38 together with lead 5 and the coupling circuitscomprised of C9, D5 and C10, D6 form a means for resetting gate means37. t I

According to the interconnections of multivibrator 38 as just described,the waveshape 2(1) is applied to input 46 to reset multivibrator 38.Multivibrator 38 is then set when input 47 receives a waveshape 2(g)diode D5. The resultant output waveshape produced at output 48 of themultivibrator 38 is shown at 2(h) and is made up of pulses 49.

Only the positive going fronts 50 of pulses 49 are passed by capacitor Cand diode D6 so that the resultant waveshape applied to the reset input45 of multivibrator 37 is made up of pulses 51 as illustrated bywaveshape 2(m). Thus it will be seen that each pulse 51 of waveshape2(m) resets multivibrator 37 and each pulse 40 of waveshape 2(1) setsmultivibrator 37 so that pulses 41, 42 and 43 produce no output at 44 ofmultivibrator 37. The output waveshape at output 44 of mu]- tivibrator37 is shown at 2(n) and includes positive going wavefronts 52corresponding to the set pulses 40 and negative going portionscorresponding to the reset pulses 51.

The output 44 of multivibrator 37 is connected to a capacitor C8 and adiode D4 to an output erminal 54 which with a circuit common terminal 55comprises a dicrotic notch output signal means. Terminals 54 and 55 areconnected to the computer 33. The diode D4 blocks the negative goingportions 53 of waveshape 2(n) thereby producing at the terminal 54relative to 55, pulses 56 as shown by waveshape 2(0) of FIG. 2.

From the foregoing, it will be seen that the circuitry of FIG. 1produces at output terminal relative to 31, a waveform 20) made up ofpulses 32 which corresponds to the initial systole. Similarly, at theoutput terminal 54 relative to 55 there appears a waveshape 2(0) made upof pulses 56, each of which corresponds'to a dicrotic notch in thearterial pressure waveform. The initial systole output pulses and thedicrotic notch output pulses are the desired discrete timing signals tobe generated by the circuitry embodying the invention and may be used ordirected to computers or other electronic equipment for studying theheart.

What is claimed is:

l. Circuitry for producing from a transducer generated electrical analogof an arterial pressure waveform an initial systole spike and a dicroticnotch spike, said circuitry comprising:

low pass filter circuit means; i

a first comparator having a first input adapted to b connected to saidtransducer and a second input adapted to be connected to said transducerthrough said low pass filter circuit means;

a second comparator having input means and output means;

unidirectional low pass filter circuit means;

means for connecting said unidirectionallow pass filter means between anoutput of said first comparator and said input means of said secondcomparator;

first unidirectional coupling means having one end connected to saidoutput means of said second comparator to provide discrete initialsystole pulses at its other end;

a differentiator circuit having input means and output means;

a third comparator having input means and-output means;

a high pass filter connected between said output means of saiddifferentiator and said input means of said third comparator;

means for connecting said input means of said differentiator to saidtrnasducer;

gate means having input means and output means;

second unidirectional coupling means connected between said output meansof said third comparator and said input means of said gate to supply setpulses to said gate;

means for resetting said gate each time the voltage applied-to saidsecond input means of said first comparator becomes greater than thevoltage applied to said second input means of said first comparator; and

third unidirectional coupling means having one end connected to saidoutput means of said gate to produce a dicrotic notch voltage pulse atits other end.

2. The circuit of claim 1 wherein each of said first, second and thirdunidirectional coupling means comprises a serially connected capacitorand diode.

3. The circuit of claim 1 wherein said differentiator circuit comprisesan operational amplifier having first and second inputs and an output;

a first capacitor and a first resistor serially connected between saidsecond input of said amplifier and said transducer, said first inputbeing connected to circuit common;

a second capacitor and a second resistor connected in parallel betweensaid output and said second input of said operational amplifier.

4. The circuit of claim 3 and including first and second zener diodesconnected in back to back relationship across said second resistor.

5. The circuitry of claim 1 and including impedance matching meansinterposed between said first comparator and said unidirectional lowpass filter.

6. The circuitry of claim 1 wherein said unidirectional low pass filtercomprises a diode and a resistor connected in parallel relationshipbetween the output of said first comparator and the input of said secondcomparator, a capacitor being connected from the input of said secondcomparator to circuit common.

7. The circuit of claim 1 wherein said gate means comprises a firstmultivibrator having an output, a set input and a reset input, saidsecond unidirectional coupling means being connected tothe set input ofthe first multivibrator, said third unidirectional coupling means beingconnected to the output of said first multivibrator; and wherein saidmeans for resetting said gate comprises a second multivibrator having anoutput, a set input and a reset input;

fourth unidirectional coupling means connected between the output ofsaid second multivibrator and 8. The circuitry of claim 7 wherein saidfourth and fifth unidirectional coupling means each comprise a seriallyconnected capacitor and diode.

9. The circuit of claim 1 wherein said first and third comparators eachcomprise an operational amplifier having an output and input means; aresistor and a zener diode serially connected between each amplifieroutput and circuit common, the output of each comparator being thevoltage between the resistor and the zener diode, said input means ofthe first amplifier being connected to said low pass filter circuit andsaid input means of the second amplifier being connected to said highpass filter.

10. The circuit of claim 9 wherein said input means of said firstamplifier comprises first and second inputs, and said low pass filtercircuit comprises a resistor having one end connected to the secondinput of said first amplifier to the other end adapted to be connectedto said transducer and a capacitor connected from said second input tocircuit common; said second input adapted to be connected to saidtransducer.

11. Apparatus for processing an electric analog voltage of an arterialpressure wave as generated by a transducer comprising;

means for filtering said electrical analog to remove components above apredetermined frequency and to introduce a time lag;

means for producing a square voltage pulse each time said electricalanalog is greater in magnitude than the filtered analog;

means causing the trailing edge of each of said square voltage pulses todecay exponentially;

means for producing a square voltage pulse each time said exponentialdecay goes below a predetermined level and lasting until the occurrenceof the leading edge of the next of said first mentioned square pulses;

initial systole output means;

means for coupling the leading edge of said second mentioned square wavepulses to said initial systole output means;

means for differentiating said electrical analog;

means for filtering the differentiated analog to remove components belowa predetermined frequency, the differentiated and filtered analog beingessentially a second derivative waveform with respect to time of saidanalog;

meansresponsive to said last named means for producing a switchingvoltage which switches from a high-to-low-to-high value in accordancewith changes in slope of said analog;

gate means; I

second coupling means for transmitting said switching voltage to aninput of said gate means;

means for opening said gate once each cycle for the first pulse receivedfrom said second coupling means to produce a square voltage pulse at anoutput of said gate;

dicrotic notch output means; and

third coupling means for passing a wave front of prdetermined polarityfrom said output of said gate means to said dicrotic notch output means.

1. Circuitry for producing from a transducer generated electrical analogof an arterial pressure waveform an initial systole spike and a dicroticnotch spike, said circuitry comprising: low pass filter circuit means; afirst comparator having a first input adapted to be connected to saidtransducer and a second input adapted to be connected to said transducerthrough said low pass filter circuit means; a second comparator havinginput means and output means; unidirectional low pass filter circuitmeans; means for connecting said unidirectional low pass filter meansbetween an output of said first comparator and said input means of saidsecond comparator; first unidirectional coupling means having one endconnected to said output means of said second comparator to providediscrete initial systole pulses at its other end; a differentiatorcircuit having input means and output means; a third comparator havinginput means and output means; a high pass filter connected between saidoutput means of said differentiator and said input means of said thirdcomparator; means for connecting said input means of said differentiatorto said transducer; gate means having input means and output means;second unidirectional coupling means connected between said output meansof said third comparator and said input means of said gate to supply setpulses to said gate; means for resetting said gate each time the voltageapplied to said second input means of said first comparator becomesgreater than the voltage applied to said second input means of saidfirst comparator; and third unidirectional coupling means having one endconnected to said output means of said gate to produce a dicrotic notchvoltage pulse at its other end.
 2. The circuit of claim 1 wherein eachof said first, second and third unidirectional coupling means comprisesa serially connected capacitor and diode.
 3. The circuit of claim 1wherein said differentiator circuit comprises an operational amplifierhaving first and second inputs and an output; a first capacitor and afirst resistor serially connected between said second input of saidamplifier and said transducer, said first input being connected tocircuit common; a second capacitor and a second resistor connected inparallel between said output and said second input of said operationalamplifier.
 4. The circuit of claim 3 and including first and secondzener diodes connected in back to back relationship across said secondresistor.
 5. The circuitry of claim 1 and including impedance matchingmeans interposed between said first comparator and said unidirectionallow pass filter.
 6. The circuitry of claim 1 wherein said unidirectionallow pass filter comprises a diode and a resistor connected in parallelrelationship between the output of said first comparator and the inputof said second comparator, a capacitor being connected from the input ofsaid second comparator to circuit common.
 7. The circuit of claim 1wherein said gate means comprises a first multIvibrator having anoutput, a set input and a reset input, said second unidirectionalcoupling means being connected to the set input of the firstmultivibrator, said third unidirectional coupling means being connectedto the output of said first multivibrator; and wherein said means forresetting said gate comprises a second multivibrator having an output, aset input and a reset input; fourth unidirectional coupling meansconnected between the output of said second multivibrator and the resetinput of said first multivibrator; fifth unidirectional coupling meansconnected between the set input of said second multivibrator and saidoutput of said first comparator; and means connecting said other end ofsaid first unidirectional coupling means to the reset input of saidsecond multivibrator.
 8. The circuitry of claim 7 wherein said fourthand fifth unidirectional coupling means each comprise a seriallyconnected capacitor and diode.
 9. The circuit of claim 1 wherein saidfirst and third comparators each comprise an operational amplifierhaving an output and input means; a resistor and a zener diode seriallyconnected between each amplifier output and circuit common, the outputof each comparator being the voltage between the resistor and the zenerdiode, said input means of the first amplifier being connected to saidlow pass filter circuit and said input means of the second amplifierbeing connected to said high pass filter.
 10. The circuit of claim 9wherein said input means of said first amplifier comprises first andsecond inputs, and said low pass filter circuit comprises a resistorhaving one end connected to the second input of said first amplifier tothe other end adapted to be connected to said transducer and a capacitorconnected from said second input to circuit common; said second inputadapted to be connected to said transducer.
 11. Apparatus for processingan electric analog voltage of an arterial pressure wave as generated bya transducer comprising; means for filtering said electrical analog toremove components above a predetermined frequency and to introduce atime lag; means for producing a square voltage pulse each time saidelectrical analog is greater in magnitude than the filtered analog;means causing the trailing edge of each of said square voltage pulses todecay exponentially; means for producing a square voltage pulse eachtime said exponential decay goes below a predetermined level and lastinguntil the occurrence of the leading edge of the next of said firstmentioned square pulses; initial systole output means; means forcoupling the leading edge of said second mentioned square wave pulses tosaid initial systole output means; means for differentiating saidelectrical analog; means for filtering the differentiated analog toremove components below a predetermined frequency, the differentiatedand filtered analog being essentially a second derivative waveform withrespect to time of said analog; means responsive to said last namedmeans for producing a switching voltage which switches from ahigh-to-low-to-high value in accordance with changes in slope of saidanalog; gate means; second coupling means for transmitting saidswitching voltage to an input of said gate means; means for opening saidgate once each cycle for the first pulse received from said secondcoupling means to produce a square voltage pulse at an output of saidgate; dicrotic notch output means; and third coupling means for passinga wave front of predetermined polarity from said output of said gatemeans to said dicrotic notch output means.